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Logo of bmcmicrBioMed Centralsearchsubmit a manuscriptregisterthis articleBMC Microbiology
 
BMC Microbiol. 2012; 12: 59.
Published online Apr 20, 2012. doi:  10.1186/1471-2180-12-59
PMCID: PMC3419637
Characterization of a novel chaperone/usher fimbrial operon present on KpGI-5, a methionine tRNA gene-associated genomic island in Klebsiella pneumoniae
Jon J van Aartsen,1 Steen G Stahlhut,2 Ewan M Harrison,1 Marialuisa Crosatti,1 Hong-Yu Ou,3 Karen A Krogfelt,2 Carsten Struve,2 and Kumar Rajakumarcorresponding author1,4
1Department of Infection, Immunity and Inflammation, University of Leicester, Leicester, LE1 9HN, UK
2Department of Microbiological Surveillance and Research, Statens Serum Institut, Artillerivej 5, 2300, Copenhagen S, Denmark
3State Key Laboratory of Microbial Metabolism, Shanghai Jiaotong University, Shanghai, 200030, P.R. China
4Department of Clinical Microbiology, University Hospitals of Leicester NHS Trust, Leicester, LE1 5WW, UK
corresponding authorCorresponding author.
Jon J van Aartsen: jjv1/at/le.ac.uk; Steen G Stahlhut: stl/at/ssi.dk; Ewan M Harrison: emh17/at/le.ac.uk; Marialuisa Crosatti: mc257/at/le.ac.uk; Hong-Yu Ou: hyou/at/sjtu.edu.cn; Karen A Krogfelt: kak/at/ssi.dk; Carsten Struve: cas/at/ssi.dk; Kumar Rajakumar: kr46/at/le.ac.uk
Received October 30, 2011; Accepted April 20, 2012.
Abstract
Background
Several strain-specific Klebsiella pneumoniae virulence determinants have been described, though these have almost exclusively been linked with hypervirulent liver abscess-associated strains. Through PCR interrogation of integration hotspots, chromosome walking, island-tagging and fosmid-based marker rescue we captured and sequenced KpGI-5, a novel genomic island integrated into the met56 tRNA gene of K. pneumoniae KR116, a bloodstream isolate from a patient with pneumonia and neutropenic sepsis.
Results
The 14.0 kb KpGI-5 island exhibited a genome-anomalous G + C content, possessed near-perfect 46 bp direct repeats, encoded a γ1-chaperone/usher fimbrial cluster (fim2) and harboured seven other predicted genes of unknown function. Transcriptional analysis demonstrated expression of three fim2 genes, and suggested that the fim2A-fim2K cluster comprised an operon. As fimbrial systems are frequently implicated in pathogenesis, we examined the role of fim2 by analysing KR2107, a streptomycin-resistant derivative of KR116, and three isogenic mutants (Δfim, Δfim2 and ΔfimΔfim2) using biofilm assays, human cell adhesion assays and pair-wise competition-based murine models of intestinal colonization, lung infection and ascending urinary tract infection. Although no statistically significant role for fim2 was demonstrable, liver and kidney CFU counts for lung and urinary tract infection models, respectively, hinted at an ordered gradation of virulence: KR2107 (most virulent), KR2107[increment]fim2, KR2107[increment]fim and KR2107[increment]fim[increment]fim2 (least virulent). Thus, despite lack of statistical evidence there was a suggestion that fim and fim2 contribute additively to virulence in these murine infection models. However, further studies would be necessary to substantiate this hypothesis.
Conclusion
Although fim2 was present in 13% of Klebsiella spp. strains investigated, no obvious in vitro or in vivo role for the locus was identified, although there were subtle hints of involvement in urovirulence and bacterial dissemination from the respiratory tract. Based on our findings and on parallels with other fimbrial systems, we propose that fim2 has the potential to contribute beneficially to pathogenesis and/or environmental persistence of Klebsiella strains, at least under specific yet-to-be identified conditions.
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